1. Field of the Invention
The present invention relates generally to fluidic flow resistive elements and more particularly to a fluidic resistive element for maintaining the Reynolds number associated with the working fluid at a substantially constant value despite small increments in the temperature of the working fluid about its operating temperature.
2. Description of the Prior Art
Fluidic devices, employing a suitable working fluid, have been developed in recent years to perform functions analogous to electronic devices. These devices have been both pneumatic and hydraulic in nature. Although many of the basic principles of fluidics apply equally as well to both gas and liquid operation, there are also important differences between the two modes of operation owing to the radically different physical properties of the working fluids involved. Pneumatic systems are designed to incorporate air or some other gas as a working fluid. The typical liquid used in hydraulic fluidic systems is MIL-H-5606 red oil. MIL-H-5606 red oil, compared to air is of higher density and viscosity but of much lower compressibility. In many hydraulic fluidic systems, the working oil is exposed to a range of temperatures. Accordingly, the viscosity and Reynolds number of the oil will, unlike air, vary drastically at normal operating pressures.
Reynolds number variation is a critical factor in many applications. For example, the gain of hydraulic fluid amplifiers, operating in the lower range of supply pressures, is much more sensitive to Reynolds number changes than equivalent devices utilizing air as the working fluid. For fixed supply pressures, as the oil temperature drops, the Reynolds number and thus the amplifier gain decreases. A similar problem is encountered in the use of hydraulic fluid flow sensors. For fixed supply pressures, as the oil temperature drops, and the Reynolds number decreases, these devices exhibit a marked null-shift.
One possible solution would be to control the temperature of the hydraulic oil. However, such an approach would be extremely difficult and expensive to carry out and limited in application to a single hydraulic fluid.
Instead of compensating for temperature changes in hydraulic oil, the present invention maintains the Reynolds number of the hydraulic oil at a substantially constant level despite small increments in the temperature of the working fluid about the operating temperature of the fluid.